#include <iostream>
using namespace std;

int my_sum(int x, int y);
int my_sum(int x, int y, int z = 100);

int main(int argc, const char *argv[]){
    //cout << my_sum(10, 20) << endl; // 有歧义 会报错
    cout << my_sum(10, 20, 30) << endl; // 60
    return 0;
}

int my_sum(int x, int y){
    return x+y;
}

int my_sum(int x, int y, int z){
    return x+y+z;
}
